Abstract
The research comprised of studying the effect composting sewage sludge with sawdust and vermicomposting with earthworm Eisenia fetida has on the degradation of 16 polycyclic aromatic hydrocarbons (PAHs). Raw rural sewage sludge prior composting was more contaminated with PAHs than urban sewage sludge, in both cases exceeding EU cutoff limits of 6 mg/kg established for land application. Dibenzo[a,h]anthracene (DBahAnt), acenaphtylene (Acy) and indeno[1,2,3-c,d]pyrene (IPyr) were predominant in rural sewage sludge, whilst the urban sewage sludge contained the highest concentrations of benzo[b]fluoranthene (BbFl), benzo[k]fluoranthene (BkFl) and indeno[1,2,3-c,d]pyrene (IPyr). Thirty days of composting with sawdust has caused a significant reduction of 16 PAHs on average from 26.07 to 4.01 mg/kg (84.6%). During vermicomposting, total PAH concentration decreased on average from 15.5 to 2.37 mg/kg (84.7%). Vermicomposting caused full degradation of hydrocarbons containing 2 and 6 rings and significant reduction of PAHs with 3 aromatic rings (94.4%) as well as with 5 aromatic rings (83.2%). The lowest rate of degradation (64.4%) was observed for hydrocarbons with 4 aromatic rings such as fluoranthene, benzo(a)anthracene, chrysene and pyrene. On the other hand, the highest level of degradation was determined for PAHs with 2 rings (100%), 3 rings (88%) and 6 aromatic rings in the molecule (86.9%) after composting with sawdust. Acenaphthene and pyrene were found to be the most resistant to biodegradation during both composting methods.
Highlights
Sewage sludge is an organic waste material which, when properly treated, may become an inexpensive source of nutrients used e.g. as a substitute of agricultural fertilizers
The aim of the research was to determine the effect of two methods of sewage sludge composting, using sawdust and vermicomposting with Eisenia fetida have on the level of polycyclic aromatic hydrocarbons (PAHs) degradation
This could be attributed to a high concentration of acenaphtylene and dibenzo[a,h]anthracene
Summary
Sewage sludge is an organic waste material which, when properly treated, may become an inexpensive source of nutrients used e.g. as a substitute of agricultural fertilizers. Since this specific waste is a by-product of wastewater treatment, its composition varies significantly depending on the origin of the incoming wastewater to the plant. Composting of the sewage sludge is decomposition (mineralization) and humification of the waste biomass. This process undergoes completion with the use of microorganisms and can be carried out in an open system heaps or in special bioreactors. It decreases the volume and mass of the sludge and it leads to the production of quality organic fertilizer
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